The present invention relates to an apparatus for stuffer box crimping a synthetic multifilament yarn which includes a ceramic nozzle.
For stuffer box crimping a multifilament yarn, known apparatus comprise a feed nozzle and a stuffer box chamber downstream of the feed nozzle. In these apparatus, the feed nozzle advances the yarn into the stuffer box chamber, wherein it is compacted to a yarn plug, and crimped. The feed nozzle is biased with a conveying medium, preferably a heated gas, which advances the yarn inside a yarn channel to the stuffer box chamber. Inside the stuffer box chamber, the yarn plug is formed. In so doing, the multifilament yarn comes to lie in loops on the surface of the yarn plug, and is compacted by the conveying medium, which is able to escape from the stuffer box chamber upstream of the yarn plug. To this end, the wall of the stuffer box chamber includes on its circumference a plurality of slotted openings, through which the conveying medium is able to leave.
To obtain a uniform crimp of the yarn, the plug formation in the stuffer box chamber proceeds with very great uniformity. In this process, the frictional forces that form by the relative movement of the yarn plug have a substantial influence on the texturing process. There exists equilibrium of forces respectively between the advancing action or impact pressure action of the conveying medium advancing from the yarn channel of the feed nozzle and the braking actions exerted on the yarn plug by frictional forces. By adjusting a conveying pressure or by adjusting a removal of the conveying medium by additional suction, it is possible to adjust or control the advancing action. In comparison therewith, the braking action generated by the friction between the yarn plug and the chamber wall is largely dependent on the condition of the chamber wall.
EP 1 060 302 discloses a device for treating yarn, which comprises a releasable screw-type connection. A treatment body constructed in two pieces consists of at least one ceramic component. When being assembled, the two components are positioned relative to each other by means of alignment pins. The treatment body is then secured to a machine frame by means of a screw extending through it. The device relates in particular to texturing nozzles, which can thus be made relatively small.
EP 1 116 806 discloses a known device for stuffer box crimping, which comprises a texturing nozzle for treating a filament-type material in a treatment channel formed between at least two overlying base bodies. In the treatment channel, the device furthermore comprises at least one nozzle body for supplying a gaseous treatment medium and at least one venting component. It is there proposed to make the treatment channel at least in sections of a more resistant material than the metallic base body. To this end, different one-piece ceramic inserts are positioned in the region of the nozzle channel. It is known that the temperature expansion coefficient varies greatly between ceramic and metallic material. Since both high temperatures and temperature fluctuations occur during the stuffer box crimping process, the device for stuffer box crimping may be subjected in operation to greatly differing thermal loads, which under circumstances cause the components of the device to shift in position and thus lead to a faulty formation of the yarn plug.
A further device for stuffer box crimping is disclosed, for example, in WO 03/004743 and corresponding U.S. Patent Publ. No. 2004/0237211, wherein a specially preferred embodiment of the device is configured such that the gas-permeable chamber wall includes on the inner side facing the yarn plug a friction surface of a wear-resistant material, in particular ceramic material. Besides the wear-resistant effect, providing a material of this type in this region also results in that the gas-permeable wall is resistant to corrosion and less susceptible to contaminations. With that, it is possible to prevent in particular yarn lubricant residues from depositing.
WO 03/004743 furthermore discloses an embodiment of a feed nozzle. The feed nozzle comprises a base body and a plurality of guide inserts in spaced relationship, which are advantageously made of a ceramic material, or which may be provided with a corresponding coating. This ensures that points of contact and friction which are greatly subject to the stress of the yarn consist of a wear-resistant material, so as to achieve a stable and uniform advance and feed of the yarn. In addition, the coefficients of friction between the yarn and the points of contact and friction are considerably reduced.
While until now the known device has turned out to be reliable, further technical problems have surfaced in connection with the objective of having devices of a simple construction, which have a long service life on the one hand, and permit a uniform production of the yarn plug on the other hand. As already disclosed in WO 03/004743 and the corresponding U.S. publication noted above, there has previously existed a need for making portions of the devices of solid ceramic, which are contacted by the yarn. This applies in particular also to the feed nozzle. A problem in this connection is that the ceramic components of the device must be assembled with additional components of the device. The cause for the technical problems essentially lies in the different thermal expansion behavior of ceramic and metal. Thus, the combination of ceramic components and metallic components presents a problem in particular where great temperature fluctuations occur. In the present case, this applies in particular to the region of the feed nozzle. In this region of the device, temperature fluctuations occur in a range from room temperature to about 300° C. At the same time, a particularly high precision in the feed or advance of the yarn is required just in this region, so that the position of the individual components relative to one another is to be maintained as exactly as possible during operation.
Based on the foregoing, it is an object of the present invention to provide means, which solve the technical problems as have been described with reference to the state of the art, at least in part, or which lessen their disadvantages.
It is also an object of the invention to provide components of a ceramic nozzle for producing yarn plugs, which can be mounted to metallic components in a durable manner and with high precision, even when considerable temperature fluctuations occur in the vicinity.
It is a further object to provide a device for stuffer box crimping a synthetic multifilament yarn with improved protection against wear with respect to yarn guiding components.